There are many fields of manufacture in which metalizing is used to provide bodies, such as bars and rods and tubes of ordinary steel, with an expensive surface layer, treatment, or coating that is fused to the metal, to provide a part that will respond to manufacturing specifications but is less expensive than making the entire body of the same material that the specifications require be only at the surface of the body. Thus, parts such as force transmitting rods, piston rods, shock absorber shafts, bearing shafts, pivot pins, tubes, and the like, are frequently required to provide thereon an exterior surface of chromium, or chrome.
It has been long known that ordinary steels, except for leaded steels or resulphurized steels, provided in bar or pin form, may be chrome surfaced, by plating or the like, to both meet the specifications for desired strength of the part and with the surface character being specially adapted for the environment in which the part is to be used.
However, chromium is a relatively expensive material, and chromium's use in various chemical baths means, by which chrome plating may be effected, is environmentally undesirable and/or difficult and expensive to control.
While metalizing the surface of bars and rods avoids, to substantial extent, the undesirable environmental effects of chemical plating such bodies, the mechanical metalizing techniques presently employed have usually used an open flame torch that burns fuel gases, such as acetylene, propane, or the like in the presence of oxygen, to both preheat the body surface to an elevated temperature and to heat the surface application material, which is initially in powder form, to a temperature at which the molten powder material will fuse with the material of the body. These prior art metalizing techniques have not been wholly successful in metalizing tubes, as the heat of a torch will frequently burn through the wall of the tube.
The problems with said prior technique are that there is both lack of accurate control of the thickness of the layer of the surface application material to the underlying body, and resultant lack of uniformity of the thickness of the layer that is applied by the torch heat. Furthermore, the minimum thickness of the layer of applied material usually obtained by metalizing with an open flame torch, working with powdered metal, is about 0.008 inches, and maximum thickness of layer of applied metal is about 0.015 inches, both of which thickness values are frequently much greater than the thickness of the applied material layer required to be supplied to meet the performance specifications for the metalized part, and this substantially increases the cost of manufacture. A further problem is that when using fine particles of metalizing materials to form a fused surface on an underlying body, the torch heat intensity is frequently so great that it vaporizes, or burns away, a substantial quantity of the finest particles of the metalizing material, resulting in loss of material and economic waste.